The purpose of the proposed project is to determine the mutational specificity of metal mutagens by utilizing the trpA system of the bacterium, Escherichia coli. Metals are among the most common of our environmental chemicals and many cancer researchers have suggested that carcinogens act by causing damage to DNA, possibly by producing somatic mutations. The methodology will involve utilizing metal mutagens to induce Trp plus revertants of the various trpA alleles. Once the revertants have been recovered, they can be placed into discrete phenotypic classes by means of simple chemical tests. By observing which revertant classes are induced by a particular metal, it is possible to deduce what particular type of mutational event is enhanced by that metal. Many mutational events, transitions, transversions, insertions and deletions can be detected with the trpA system. When the mutational specificity of a metal is revealed, it is hoped that this information will provide further insight into the mode of carcinogenesis.